The invention relates to an instrument for high-precision mechanical applications or for medical applications (e.g. surgery, endovascular procedures, or for use as an endoscope) of a minimally invasive nature, comprising a hollow tubular member (1) having a proximal bendable zone (4) that forms a controller head, a distal bendable zone (5) that forms an effector—a steerable tip—and flexes responsive to movements of the controller, and, a bend-resistive zone (6) between the aforementioned zones (4, 5), that transmits movements of the controller to the effector. The member is preferably formed from one or more substantially solid walled tubes. The high-precision instrument find applications where exquisite, remote movements in confined spaces are needed, such as in medical applications, and in the inspection and repair of encased devices such as engines, pipelines, valves and other mechanical systems.
The notion an instrument having a steerable tip is known in the art. For instance, WO 03/037416 describes a mechanism that deflects portions of a flexible body such as a catheter in more than one direction in a single plane, as well as in more than one plane by use of a pullwire. In order to control the deflection of the distal end, many designs incorporate one or more steering cables. Mostly these cables are fed through guide-sleeves located in the wall of the tube or in its lumen. These guide-sleeves that hold the steering cables in place are bulky and add to the cross-section of the wall.
For example, US-A-2006/0178556 (See FIGS. 1A and 1C), describes a steerable device having a ring of longitudinally extending cables connecting to the head, which cables are fixedly secured in the radial direction. A disadvantage of this instrument is, however, that the cables are fed through guide-sleeves provided in the longitudinal direction of the cables, which increase the diameter of the instrument.
A system to omit these sleeves has been described in WO 02/13682 (see FIGS. 1B and 1D) which discloses a steerable device also of a ring of cables comprising longitudinally extending cables connected to the head, which cables are fixedly secured in the radial direction. Instead of the cables being fed through guide-sleeves as in US-A-2006/0178556, they are disposed side by side so filling the space where the guide sleeves would otherwise be. A disadvantage of this system is the high construction cost for devices where lumen diameters need to be maximised for a given outer diameter—i.e. the walls made thin which is a requirement for most applications. A rapid increase in the number of steering wires is seen when increasing the internal diameter while maintaining a thin wall, for example, 25 steering cables of 0.2 mm for a lumen of 1 mm diameter. Furthermore, the alignment and correct pre-tensioning of a large number of narrow diameter wires represents an enormous technical challenge. Further it is anticipated that the wires of narrowed diameter may slip circumferentially within the sleeve, and tangle or wear.
It remains challenging to make an adequate affixation with the head and tip. Standard affixation techniques include soldering, clamping, crimping, use of small bolts, glue, knotting, cable U-turns through rigid termination disk or laser-welding. Mostly these affixation techniques result in bulky joints and some of them even weaken the wires.
Additionally, a compression spring is used in the art to pre-stress the tip, however, this reduces its torsion and bending stability, meaning the tip can readily be deflected from a bent position by the application of an external force to the tip. Moreover, axial compression, for example, by pulling the tool control wire during operation of the surgical tool can induce straightening of the tip—a phenomenon known as crosstalk which is to be avoided.
One particular application of a steerable tube is in the field of neurosurgery. Neurosurgical endoscopic intraventricular procedures are typically performed with a neurosurgical instrument known as the Caemaert endoscope. It is a long rigid shaft with an external diameter of ˜6 mm and four lumens. One lumen is for an optic element, one for a working channel, and two for rinsing fluid. The endoscope is introduced through a burr hole in the skull; the shaft intrudes the brain tissue at a non-eloquent area before entering the fluid filled ventricles. To reach the most central ventricle—known as the third ventricle—passage through an important ring-like structure, the foramen of Monroe, is necessary. Damage to this structure causes amnesia. Access to the third ventricle allows several surgical procedures to be performed such as perforating membranes or removing tumors. The latter is the most challenging procedure, requiring the sequential use of coagulation, grasping and aspiration. Using present technology, it is not possible to have more than one steerable tube inside the endoscopic shaft, especially when one of the tubes is a steerable aspiration catheter which also requires a large lumen compatible with removal of particles of tissue.
The present invention, therefore, address the problems of the art by providing a steerable tube having a large diameter lumen while minimizing the outer diameter, which is reliable and cost-effective to manufacture.